[12][13] Later that year, Kocian was selected to make her international debut at the Top Gym Invitational in Charleroi, Belgium.

[14] Kocian began the 2010 season at the WOGA Classic where she finished second in the all-around to her club teammate Grace McLaughlin.

[18] At the City of Jesolo Trophy, she won a gold medal with the American team and finished second in the all-around to Kyla Ross.

[22] At the U.S. Classic, held in Hoffman Estates, Illinois, she placed seventh all-around and earned a silver medal on the uneven bars behind Kyla Ross.

[26] At the City of Jesolo Trophy, she stuck her full-twisting double back dismount to win the uneven bars gold medal.

[32] On September 17, Kocian was selected to compete at the 2014 World Championships in Nanning, China, alongside Locklear, Alyssa Baumann, Simone Biles, Kyla Ross, and Mykayla Skinner.

[38] Kocian was selected to compete at the World Championships in Glasgow, alongside Simone Biles, Gabby Douglas, Brenna Dowell, Maggie Nichols, and Aly Raisman.

[39] During the qualification round, Kocian competed on the balance beam and on the uneven bars, where she qualified for the event final in third place.

[41] In the uneven bars final, she scored a 15.366, placing her in an unprecedented four-way tie for the gold medal with Russians Viktoria Komova, Daria Spiridonova, and China's Fan Yilin.

[42] Kocian began the Olympic season at the WOGA Classic and competed on the uneven bars and balance beam, winning the gold medals in both events.

[50] On July 10, 2016, Kocian was named to the U.S. team for the 2016 Olympic Games alongside Simone Biles, Gabby Douglas, Aly Raisman, and Laurie Hernandez.

[54] Kocian's uneven bars score tied with Russia's Aliya Mustafina the highest of the team final.

[55] On August 14, Kocian won a silver medal in the uneven bars event final, scoring 15.833 and finishing behind Mustafina by only 0.067.

[56][57] Kocian began attending the University of California, Los Angeles in the fall of 2016 and joined the UCLA Bruins gymnastics program.

[63] On August 21, 2017, Kocian underwent surgery to repair her torn labrum, an injury she had dealt with since the 2016 Olympic Trials.

[65] She added floor exercise to her repertoire on February 25 in a dual meet against Oregon State,[66] and she returned to competing on uneven bars at the NCAA Regional Championship on April 7.

[68] During the Super Six finals, she fell on the balance beam but contributed great performances on uneven bars and floor exercise to help UCLA win their first NCAA Gymnastics title since 2010.

[78] On March 12, all remaining competitions for the season were canceled due to the COVID-19 pandemic in the United States, including UCLA's senior night and the entire post-season.

[81] She was also named as the Bruins' Tom Hansen Medal recipient alongside football player Darnay Holmes.

[1] On August 16, 2018, Kocian came forward as a survivor of Larry Nassar's sexual abuse alongside UCLA teammate Kyla Ross.

Kocian also shared that she did not feel supported by USA Gymnastics and described a toxic culture that led to her being afraid to speak out about the abuse.